Molecular Ecology (2005) 14, 171–178 doi: 10.1111/j.1365-294X.2004.02380.x © 2004 Blackwell Publishing Ltd Blackwell Publishing, Ltd. Colonization history of the high-arctic pink-footed goose Anser brachyrhynchus M. RUOKONEN,* T. AARVAK † and J. MADSEN ‡ *Department of Biology, P.O. Box 3000, FIN-90014 University of Oulu, Finland, †Norwegian Ornithological Society, Sandgata 30 B, N-7012 Trondheim, Norway, ‡National Environmental Research Institute, P.O. Box 358, DK-4000 Roskilde, Denmark Abstract Population structure and phylogeography of the pink-footed goose, Anser brachyrhynchus Baillon 1833, was studied using mtDNA control region sequences (221 bp) from 142 indi- viduals. Present breeding areas of the species in Greenland, Iceland, and Svalbard were largely covered by ice during the late Pleistocene. In pairwise comparisons φ ST estimates showed significant differentiation among eastern and western populations, whereas sam- pling localities within both areas were not differentiated. The mtDNA data indicate that the populations have separated recently (less than 10 000 years ago) and present breeding areas were colonized from one refugial population. The levels of haplotype and nucleotide diversity were approximately five times higher for the eastern population compared to the western population and suggest that the latter was colonized by a subset of eastern birds. Time to the most recent common ancestor of the species is 32 000 – 46 000 years, i.e. the present mtDNA variation of the pink-footed goose has accumulated during the last 0.1 My. Estimates of the long-term female effective population size (5400 –7700 for the eastern popu- lation) imply that the refugial population of the pink-footed goose has been large. Tundra habitats were more extensive in cold periods of the late Pleistocene than today and may have sustained population sizes that allowed the accumulation of extant genetic polymorph- ism. It is not probable that the postulated small refugial areas in the high latitudes had a significant role in maintaining this diversity. Keywords: Anser brachyrhynchus, mtDNA, northern refugia, phylogeography, pink-footed goose, Pleistocene Received 12 August 2004; revision received 22 September 2004; accepted 22 September 2004 Introduction The pink-footed goose (Anser brachyrhynchus Baillon 1833) is a high-arctic species inhabiting areas that were largely covered by glaciers during the cold periods of the last ice age. The present breeding range of the species is limited to Svalbard, Iceland, and Greenland. Although the pink- footed goose is monotypic based on morphology, the species is considered to consist of two populations (Cramp & Simmons 1977). The western population breeds in the central parts of Iceland and the east coast of Greenland. Greenland birds leave in late August to join the breeding birds of Iceland and they migrate together to the British Isles to over-winter (Ogilvie & Boyd 1976; Mitchell et al . 1999). The eastern population of the pink-footed goose breeds in Svalbard and migrates south via Norway to the wintering areas in Denmark, the Netherlands, and Belgium (Madsen et al . 1999). Western and eastern populations have been considered demographically independent with few individuals dispersing between the populations ( Webbe 1958; Mitchell et al . 1999). Coinciding with the recent popu- lation increases, the wintering ranges of the populations have come closer, possibly increasing the current rate of exchange between the populations. Based on ringing results, annual exchange rates of 0.1% – 0.8% (Ebbinge et al . 1984) and 0.7% (Madsen et al . 1999) between the two populations have been reported. However, these estimates are mainly based on observations at the nonbreeding areas, and thus it is not known if the birds are recruited to the breeding population. Ice ages are among the most important historical factors in affecting the structuring and levels of variation in present populations. Well-known Late Pleistocene (0.13 – 0.01 Mya) Correspondence: Minna Ruokonen, Fax: + 35885531061; E-mail: minna.ruokonen@oulu.fi